CN106813901A - The measurement apparatus and its measuring method of optics phase-delay quantity - Google Patents

Abstract

A measuring device and method for measuring the phase delay of an optical device, the device mainly includes a dual-frequency He-Ne laser, a polarizing beam splitter, a half-wave plate, a 45° high reflection mirror, a polarizing plate, and a photodetector. Using heterodyne detection technology, the linearly polarized light passes through the fast axis and slow axis of the optical device to be tested, and beats with the reference frequency light respectively, uses a photodetector to receive the beat frequency signal, and compares the phase difference of the beat frequency signal to realize the phase of the phase device Accurate measurement of latency. The invention can measure the phase delay of any wave band of the optical device, and has the characteristics of simple and compact structure, convenient use, strong anti-environment interference ability, easy integration and accurate measurement of the phase delay.

Description

Measuring device and method for phase retardation of optical device

technical field

The invention relates to the field of precision measurement, in particular to a measuring device and a measuring method for the phase delay of an optical device.

Background technique

As an important part of precision instruments, optical devices such as half-wave plates and quarter-wave plates have important applications in precision measurement, laser technology and other fields. Whether the phase delay is consistent with the nominal value has a great influence on the performance of the instrument, so it is of great significance to accurately measure the phase delay of half-wave plates and quarter-wave plates.

Phase delay devices are usually made of materials with birefringence effect, and the phase delay is proportional to 2π( _ne -n _o )d/λ, where _ne and n _o are the difference between extraordinary light and ordinary light in crystal materials Refractive index, d is the thickness of the wave plate, and λ is the wavelength of light used. Many experts and scholars in the past have proposed different measurement schemes, the patent number is ZL201320548522.6, and the name of the utility model is "a device for measuring wave plate phase delay by laser frequency method". The principle of laser frequency splitting makes one oscillation frequency of the laser become two oscillation frequencies, and the frequency difference between these two frequencies is proportional to the phase delay of the wave plate. The frequency difference between the two split frequencies is measured to obtain the phase delay of the wave plate. The patent number is ZL201210073614.3, and the title of the invention is "A Method for Measuring the Phase Delay Angle of an Optical Device". Different, by measuring the long-axis azimuth angle of the transmitted or reflected light to deduce the phase delay of the device under test.

Contents of the invention

The object of the present invention is to provide an accurate measurement device for the phase delay of an optical device. The difference from the existing test scheme is that the phase difference of the linearly polarized light passing through the fast axis and slow axis of the optical device is directly detected, and the detected phase difference is the phase delay of the optical device. The measuring device can measure the phase delay of any wavelength band of the optical device, and has the characteristics of simple and compact structure, convenient use, strong anti-environment interference ability, easy integration and accurate phase delay measurement.

Technical solution of the present invention is as follows:

A measuring device for the phase retardation of an optical device is characterized in that it includes a dual-frequency He-Ne laser, and the direction of the two-frequency (f ₁ , f ₂ ) laser light emitted by the dual-frequency He-Ne laser is the first polarization beam splitter , wherein the horizontally polarized f ₁ laser is transmitted and propagated through the first polarization beam splitter, and the vertically polarized f ₂ laser is reflected and propagated through the first polarization beam splitter, along the f ₁ light is followed by the first half-wave plate, the first 45° high Reflective mirror, second polarizing beam splitter, second polarizing plate, second photodetector, followed by the second half-wave plate, second 45° high reflective mirror, second polarizing beam splitting mirror, first polarizing plate along f ₂ light , the first photodetector, the installation direction of the fast axis of the first half-wave plate forms an included angle of 22.5° with the horizontal plane, the installation direction of the fast axis of the second half-wave plate forms an included angle of 67.5° with the horizontal plane, and the first The light transmission directions of the first polarizer and the second polarizer form an included angle of 45° with the horizontal plane.

The method for measuring the phase delay of the optical device by using the above-mentioned measuring device for the phase delay of the optical device comprises the following steps:

1) the optical device to be tested is placed in the optical path between the first half-wave plate and the second polarizing beam splitter, and the fast axis of the device to be tested is parallel to the horizontal plane, and the slow axis is perpendicular to the horizontal plane;

2) Start the dual-frequency He-Ne laser, the first photodetector and the second photodetector respectively obtain the beat frequency signal _E9 , and the beat frequency signal _E11 is as follows:

E ₉ ＝A"B′cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ"]

E ₁₁ ＝A′B"cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ′];

3) Comparing the photodetector output signals E ₉ and E ₁₁ , the size of δ=δ′-δ" can be obtained, which is the phase delay of the optical device to be tested; that is, by comparing the first photodetector and the second The phase difference of the light beat frequency signal responded by the photodetector can be used to obtain the phase delay of the device under test;

4) The phase retardation of the optical device to be tested is proportional to 2π(n _e -n _o )d/λ, where n _e and n _o are the refractive indices of extraordinary light and ordinary light of the crystal material, d is the thickness of the device, and λ is incident light wavelength.

5) When the wavelength of the optical device to be tested is inconsistent with the wavelength of the dual-frequency He-Ne laser, the following relationship δ _real = δ _mea * λ _He-Ne / λ _real is satisfied

In the formula, δ _real is the actual phase delay of the optical device, δ _mea is the measured phase delay, λ _He-Ne is the wavelength of the dual-frequency He-Ne laser, and λ _real is the actual wavelength of the optical device to be tested.

The invention can measure the phase delay of any wave band of the optical device, and has the characteristics of simple and compact structure, convenient use, strong anti-environment interference ability, easy integration and accurate measurement of the phase delay.

Description of drawings

Fig. 1 is the optical path diagram of the optical device phase retardation measurement device of the present invention

Figure 2: Schematic diagram of the measurement method for phase retardation of optical devices

detailed description

The technical solution in the embodiment of the present invention will be described completely and in detail below in combination with FIG. 2 in the embodiment of the present invention.

Please refer to Fig. 1 first, as can be seen from the figure, the measuring device of the optical device phase delay of the present invention comprises a dual-frequency He-Ne laser 1, and the two-frequency (f ₁ , f ₂ ) emitted by the dual-frequency He-Ne laser 1 The laser direction is the first polarization beam splitter 2, wherein the horizontally polarized f ₁ laser is transmitted and propagated through the first polarization beam splitter 2, and the vertically polarized f ₂ laser is reflected and propagated through the first polarization beam splitter 2, and the light along f ₁ is sequentially The first half-wave plate 3, the first 45 ° high reflection mirror 4, the second polarizing beam splitter 7, the second polarizer 10, the second photodetector 11, along the f ₂ light is followed by the second half-wave plate 5, the first Two 45 ° high reflection mirror 6, the second polarization beam splitter 7, the first polarizer 8, the first photodetector 9, the fast axis installation direction of the first half-wave plate 3 forms an angle of 22.5 ° with the horizontal plane, so The installation direction of the fast axis of the second half-wave plate 5 forms an angle of 67.5° with the horizontal plane, and the light transmission directions of the first polarizer 8 and the second polarizer 10 form an angle of 45° with the horizontal plane.

The specific measurement steps are as follows:

1) placing the optical device under test (12) in the optical path between the first half-wave plate 3 and the second polarizing beam splitter 7, and making the fast axis of the device under test 12 parallel to the horizontal plane, The slow axis is perpendicular to the horizontal plane;

The two-frequency light (f ₁ f ₂ ) emitted by the dual-frequency He-Ne laser 1 passes through the first polarization beam splitter 2, wherein the horizontally polarized f ₁ light is transmitted and propagated through the first polarization beam splitter 2, and the vertically polarized f ₂ light After being reflected and propagated by the first polarizing beam splitter 2, the two-frequency light can be expressed by the following formula:

E ₁ ＝Acos(ω ₁ tk _1z -φ ₁ )

E ₂ ＝Bcos(ω ₂ tk ₂ z-φ ₂ )

Among them, ω ₁ ＝2πf ₁ , ω ₂ ＝2πf ₂ , k ₁ ＝2π/λ ₁ , k ₂ ＝2π/λ ₂ , A and B are the two frequency light amplitudes respectively, φ ₁ and φ ₂ are the volume frequency light initial phase.

After f ₂ light passes through the second half-wave plate 5, the polarization direction is 45° to the horizontal plane, and the light path is turned by 90° through the second 45° high-reflection mirror 6 and is incident on the second polarizing beam splitter 7 to be divided into two components, wherein the horizontally polarized component After the second polarizing beam splitter 7 is transmitted to the first polarizer 8 and is incident on the first photodetector 9, let it be E ₃ , the vertically polarized component is reflected by the second polarizing beam splitter 7 to the second polarizing plate 10 and is incident on the first photodetector 9. Two photodetectors 11, let it be E ₄ , then E ₃ and E ₄ can be expressed by the following formula

E ₃ ＝B′cos(ω ₂ tk ₂ z-φ ₂ -Ф ₂ -Ф′)

E ₄ ＝B"cos(ω ₂ tk ₂ z-φ ₂ -Ф ₂ -Ф")

Among them, B' and B" are the amplitudes of the two components of light transmitted to the first photodetector and the amplitude of the second photodetector respectively, and _Ф2 is the f2 light incident on the _second polarizing beam splitter after passing through the first polarizing beam splitter 2 The phase change brought by the polarization beam splitter 7, Ф' is the phase change caused by the horizontal polarization component passing through the second polarization beam splitter 7 and incident on the first photodetector 9, and Ф" is the phase change caused by the vertical polarization component passing through the second polarization beam splitter 7 The phase change brought about by the incident on the second photodetector 11 after being reflected by the two polarization beam splitters 7 .

After f ₁ light passes through the first half-wave plate 3, its polarization direction is 45° with the horizontal plane, after passing through the optical device 12 to be tested, it passes through the first 45° high-reflection mirror 4, and the optical path turns 90° and enters the second polarizing beam splitter 7 to split Two components, wherein the component passing through the fast axis direction of the optical device to be tested passes through the second polarizing beam splitter 7 and is transmitted to the second polarizer 10 and enters the second photodetector 11, which is set as E ₅ . The component in the axial direction is reflected by the second polarizing beam splitter 7 to the first polarizer 8 and incident on the first photodetector 9. Let it be E ₆ , then E ₅ and E ₆ can be expressed by the following formula:

E ₅ ＝A′cos(ω ₁ tk ₁ z-φ ₁ -Ф ₁ -Ф"-δ′)

E ₆ ＝A"cos(ω ₁ tk ₁ z-φ ₁ -Ф ₁ -Ф′-δ")

Among them, A' and A" are the amplitudes of the two components of light after they are transmitted to the photodetector, Ф ₁ is the phase change brought about by f ₁ light passing through the first polarizing beam splitter 2 and entering the second polarizing beam splitter 7, Ф' is the phase change caused by the component in the fast axis direction of the optical device 12 to be tested after passing through the second polarizing beam splitter 7 and incident on the second photodetector 11, and Ф" is the phase change caused by the component in the direction of the slow axis of the optical device to be tested after passing through the second polarizing beam splitter 7. The phase change brought about by the polarization beam splitter 7 incident on the first photodetector 9 after reflection, δ' and δ" are the phase changes brought about by f ₁ light passing through the fast axis and slow axis of the optical device under test respectively.

The light components E ₃ and E ₆ incident to the first photodetector 9 perform beat frequency, and the beat frequency signal is denoted as E ₉ , and the light components E ₄ and E ₅ incident to the second photodetector 11 perform beat frequency, which The beat frequency signal is denoted as E ₁₁ . Due to the high optical frequency, the photodetector can only respond to the difference frequency signal in the beat frequency signal, then E ₉ and E ₁₁ can be expressed by the following formula

E ₉ ＝A"B′cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ"]

E ₁₁ ＝A′B"cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ′]

3) By comparing the photodetector output signals E ₉ and E ₁₁ , the magnitude of δ=δ′-δ" can be obtained, which is the phase delay of the optical device to be tested;

4) The phase retardation of the optical device to be tested is proportional to 2π(n _e -n _o )d/λ, where n _e and n _o are the refractive indices of extraordinary light and ordinary light of the crystal material, d is the thickness of the device, and λ is incident light wavelength;

5) When the wavelength of the optical device to be tested is inconsistent with the wavelength of the dual-frequency He-Ne laser, the following relationship δ _real = δ _mea * λ _He-Ne / λ _real is satisfied

In the formula, δ _real is the actual phase delay of the optical device, δ _mea is the measured phase delay, λ _He-Ne is the wavelength of the dual-frequency He-Ne laser, and λ _real is the actual wavelength of the optical device to be tested.

Experiments show that the invention can measure the phase delay of any wave band of the optical device, and has the characteristics of simple and compact structure, convenient use, strong anti-environment interference ability, easy integration and accurate phase delay measurement.

Claims (2)

1. A measuring device of optical device phase retardation is characterized in that: comprise dual-frequency He-Ne laser (1), two frequencies (f ₁ , f ₂ ) sent by this dual-frequency He-Ne laser (1) The laser direction is the first polarizing beam splitter (2), wherein the horizontally polarized f1 laser is transmitted and propagated through the _first polarized beam splitter ( ₂ ), and the vertically polarized f2 laser is reflected and propagated through the first polarized beam splitter (2), Along the f1 light are the _first half-wave plate (3), the first 45 ° high reflection mirror (4), the second polarization beam splitter (7), the second polarizer (10), the second photodetector (11 ), followed by the second half-wave plate (5), the second 45° high reflection mirror (6), the second polarizing beam splitter (7), the first polarizer (8), and the first photodetector along f ₂ light (9), the installation direction of the fast axis of the first half-wave plate (3) forms an angle of 22.5° with the horizontal plane, and the installation direction of the fast axis of the second half-wave plate (5) forms an angle of 67.5° with the horizontal plane, The light transmission direction of the first polarizer (8) and the second polarizer (10) forms an included angle of 45° with the horizontal plane. 2. Utilize the measurement device of optical device phase delay described in claim 1 to carry out the measuring method of optical device phase delay, it is characterized in that the method comprises the following steps: 1) Place the optical device to be tested (12) in the optical path between the first half-wave plate (3) and the second polarizing beam splitter (7), and make the device to be tested (12) The fast axis is parallel to the horizontal plane, and the slow axis is perpendicular to the horizontal plane; 2) Start the dual-frequency He-Ne laser (1), the first photodetector (9) and the second photodetector (11) respectively obtain the beat frequency signal E ₉ , the beat frequency signal E ₁₁ is as follows : E ₉ ＝A"B′cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ"] E ₁₁ ＝A′B"cos[(ω ₁ -ω ₂ )t-(k ₁ -k ₂ )z-(φ ₁ -φ ₂ )-(Ф ₁ -Ф ₂ )-δ′]; 3) Comparing the output signals E ₉ and E ₁₁ of the photodetector, the magnitude of δ=δ′-δ" can be obtained, which is the phase delay of the optical device to be tested; 4) The phase retardation of the optical device to be tested is proportional to 2π(n _e -n _o )d/λ, where n _e and n _o are the refractive indices of extraordinary light and ordinary light of the crystal material, d is the thickness of the device, and λ is incident light wavelength. 5) When the operating wavelength of the optical device (12) to be tested is inconsistent with the wavelength of the dual-frequency He-Ne laser, the following relationship δ _real = δ _mea * λ _He-Ne / λ _real is satisfied In the formula, δ _real is the actual phase delay of the optical device, δ _mea is the measured phase delay, λ _He-Ne is the wavelength of the dual-frequency He-Ne laser, and λ _real is the actual wavelength of the optical device to be tested.